Multimedia model

Multimedia models can describe the distribution of a chemical between environmental compartments in a state of equilibrium. Equilibrium concentrations in different environmental compartments following the release of defined quantities of pollutant may be estimated by using distribution coefficients such as and H s (see Section 3.1). An alternative approach is to use fugacity (f) as a descriptor of chemical quantity (Mackay 1991). Fugacity has been defined as fhe fendency of a chemical to escape from one phase to another, and has the same units as pressure. When a chemical reaches equilibrium in a multimedia system, all phases should have the same fugacity. It is usually linearly related to concentration (C) as follows ... 

Examples of the need for multimedia models are found in contemporary problem areas. Polynuclear aromatic hydrocarbons and metals are emitted into the atmosphere as trace impurities with the products of coal combustion. The organics have low vapor pressure and partially condense on emitted particulates in a stack plume. The particulates are transferred to the soil by dry deposition, rainout or washout. The metals manifest... 

Model Types. If it is determined that exposure pathways of interest intersect more than one of the media, the analyst is faced with the need to link together single media models (or to apply existing multimedia models). Despite claims to the contrary, there is probably no single model that is appropriate to all problems. Thus, a hybrid combination of boundary... 

One weakness of some multimedia models that must be considered by the user is inconsistency of time scales. For example, if we employ monthly averaged air concentrations to get rainout values on fifteen-minute interval inputs to a watershed model, large errors can obviously occur. The air-land-water-simulation (ALWAS) developed by Tucker and co-workers (12) overcomes this limitation by allowing for sequential air quality outputs to provide deposition data to drive a soil model. This in turn is coupled to a surface water model. 

Tucker, W.A., Eschenroeder, A.Q., and Magil, G.C., "Air Land Water Analysis System (ALWAS) A Multimedia Model for Assessing the Effect of Airborne Toxic Substances on Surface Water Quality," Arthur D, Little, Inc. report to EPA, Contract G8-03-2898, 1981 (in preparation soon to be available from NTIS or from W.A. Tucker in abbreviated form as "The Air, Land, Water Analysis System (ALWAS) ... 

To address media-specific problems, single-media models for air, surface water, groundwater and soil pollution have been developed and used by different disciplines. Although these models generally provide detailed description of the pollutant distribution in space and time and incorporate mass transfer from other media as boundary conditions, they are not capable of characterizing the total environmental impact of a pollutant release. Multimedia models have been, therefore, developed to predict the concentration of chemicals in multiple environmental media simultaneously with consideration of chemical transport and transformation within and among media [1],... 

In this chapter, a brief description of the concepts and tools available for multimedia modelling to support the environmental risk assessment is given. The environmental fate assessment is the base of a more complex study, the... 

Based on the descriptions of spatial variation in each environmental compartment, multimedia models can be categorized into multimedia compartmental models (MCMs) [3-20], spatial multimedia models (SMs) [21-24] and spatial multimedia compartmental models (SMCMs) [25-27]. MCMs assume homogeneous landscape properties in each medium and assume all environmental compartments are well mixed. SMs are collections of single-media models in which the output of one model serves as the input to the others. Each individual model in the SMs is a spatial model describing the variation of environmental properties in one or more directions. SMCMs are similar to MCMs, but consider one or more environmental compartments as nonuniform regions. 

Principal characteristics Multimedia model with steady-state condition... 

Multimedia model for fate and exposure analyses of chemicals Ecotoxicological effects Not considered... 

Multimedia model for fate analysis and extensive analysis of exposure pathways Human toxicity... 

Multimedia model focused on the primary food chain... 

FUN tool is a new integrated software based on a multimedia model, physiologically based pharmacokinetic (PBPK) models and associated databases. The tool is a dynamic integrated model and is capable of assessing the human exposure to chemical substances via multiple exposure pathways and the potential health risks (Fig. 9) [70]. 2-FUN tool has been developed in the framework of the European project called 2-FUN (Full-chain and UNcertainty Approaches for Assessing Health Risks in FUture ENvironmental Scenarios www.2-fun.org). 

The multimedia model present in the 2 FUN tool was developed based on an extensive comparison and evaluation of some of the previously discussed multimedia models, such as CalTOX, Simplebox, XtraFOOD, etc. The multimedia model comprises several environmental modules, i.e. air, fresh water, soil/ground water, several crops and animal (cow and milk). It is used to simulate chemical distribution in the environmental modules, taking into account the manifold links between them. The PBPK models were developed to simulate the body burden of toxic chemicals throughout the entire human lifespan, integrating the evolution of the physiology and anatomy from childhood to advanced age. That model is based on a detailed description of the body anatomy and includes a substantial number of tissue compartments to enable detailed analysis of toxicokinetics for diverse chemicals that induce multiple effects in different target tissues. The key input parameters used in both models were given in the form of probability density function (PDF) to allow for the exhaustive probabilistic analysis and sensitivity analysis in terms of simulation outcomes [71]. 

Integrated tool coupling an environmental multimedia model and PBPK models Human toxicity... 

Ryan PA (1985) Multimedia modelling of environmental transport. MS Thesis, University of Califomiain Los Angeles... 

Coulibaly L (1999) Multimedia modeling of organic contaminants in the Passaic river watershed. Dissertation, Department of Civil and Environmental Engineering, New Jersey Institute of Technology... 

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